What am I doing wrong?

I’m tired of giving my all to someone and opening up to them and letting them in just for them to decide I’m not worth it anymore and leave me. It hurts. Idk what I’m doing wrong. They treat me sweet at first and then things go downhill after that. I thought this time it would be different. We had SO MUCH in common, literally never a dull moment. I felt peace w/ him. We both shared our darkest secrets. And then boom, one huge argument and he decides he’s done😔. I just want to find that right person. Why does everyone else around me get to be happy and in love but with me, it seems like it’s not meant for me 💔 tired of wasting my time and investing my feelings. I’m just done trying.